Piecewise RF Power Systems and Methods for Supplying Pre-Distorted RF Bias Voltage Signals to an Electrode in a Processing Chamber

ABSTRACT

A radio frequency power system is provided that includes bias modules, a switch, a matching network, and a control module. The bias modules are configured to generate respectively DC bias voltages. The switch is configured to (i) receive current from the bias modules, and (ii) control flow of the current from the bias modules to generate a radio frequency bias voltage signal. The matching network is configured to (i) receive the radio frequency bias voltage signal, and (ii) based on the radio frequency bias voltage signal, supply at least a portion of a radio frequency output voltage signal to an electrode of a substrate support in a processing chamber. The control module is connected to the switch and configured to control a state of the switch based on the radio frequency output voltage signal to shape a waveform of the radio frequency bias voltage signal.

FIELD

The present disclosure relates to radio frequency bias potential controlsystems for processing chambers.

BACKGROUND

The background description provided here is for the purpose of generallypresenting the context of the disclosure. Work of the presently namedinventors, to the extent it is described in this background section, aswell as aspects of the description that may not otherwise qualify asprior art at the time of filing, are neither expressly nor impliedlyadmitted as prior art against the present disclosure.

Plasma etching is frequently used in semiconductor fabrication. Inplasma etching, ions are accelerated by an electric field to etchexposed surfaces on a substrate. The electric field is generated basedon RF power signals generated by a radio frequency (RF) generator of aRF power system. The RF power signals generated by the RF generator mustbe precisely controlled to effectively execute plasma etching.

A RF power system may include a RF generator, a matching network, and aload (e.g., a plasma chamber). The RF generator generates RF powersignals, which are received at the matching network. The matchingnetwork matches an input impedance of the matching network to acharacteristic impedance of a transmission line between the RF generatorand the matching network. This impedance matching aids in maximizing anamount of power forwarded to the matching network (“forward power”) andminimizing an amount of power reflected back from the matching networkto the RF generator (“reverse power”). Forward power may be maximizedand reverse power may be minimized when the input impedance of thematching network matches the characteristic impedance of thetransmission line.

In the RF power source or supply field, there are typically twoapproaches to applying the RF signal to the load. A first, moretraditional approach is to apply a continuous wave signal to the load.In a continuous wave mode, the continuous wave signal is typically asinusoidal wave that is output continuously by the power source to theload. In the continuous wave approach, the RF signal assumes asinusoidal output, and the amplitude and/or frequency of the sinusoidalwave can be varied in order to vary the output power applied to theload.

A second approach to applying the RF signal to the load involves pulsingthe RF signal, rather than applying a continuous wave signal to theload. In a pulse mode of operation, a RF sinusoidal signal is modulatedby a modulation signal in order to define an envelope for the modulatedsinusoidal signal. In a conventional pulse modulation scheme, the RFsinusoidal signal typically is output at a constant frequency andamplitude. Power delivered to the load is varied by varying themodulation signal, rather than varying the sinusoidal, RF signal.

In a typical RF power supply configuration, output power applied to theload is determined by using sensors that measure the forward andreflected power or the voltage and current of the RF signal applied tothe load. Either set of these signals is analyzed in a typical controlloop. The analysis typically determines a power value which is used toadjust the output of the RF power supply in order to vary the powerapplied to the load. In a RF power delivery system, where the load is aplasma chamber, the varying impedance of the load causes a correspondingvarying power applied to the load, as applied power is in part afunction of the impedance of the load.

In plasma systems, power is typically delivered in one of twoconfigurations. In a first configuration, the power is capacitivelycoupled to the plasma chamber. Such systems are referred to ascapacitively coupled plasma (CCP) systems. In a second configuration,the power is inductively coupled to the plasma chamber. Such systems aretypically referred to as inductively coupled plasma (ICP) systems.Plasma delivery systems typically include a bias power and a sourcepower applied to one or a plurality of electrodes. The source power istypically used to generate the plasma and the bias power is typicallyused to tune the plasma to an energy level relative to a bias RF powerlevel. The bias and the source may share the same electrode or may useseparate electrodes, in accordance with various design considerations.

When a RF power delivery system drives a load in the form of a plasmachamber, the electric field generated by the power delivered to theplasma chamber results in ion energy within the chamber. The ion energyis distributed non-uniformly due to particle drift/diffusion effects andthe externally applied fields. One characteristic measure of ion energyis the ion energy distribution function (IEDF). The ion energydistribution function (IEDF) at the substrate surface can be controlledwith a RF waveform. One way of controlling the IEDF for a system inwhich multiple RF power signals are applied to the load occurs byvarying multiple RF signals that are related by frequency and phase. Thefrequencies between the multiple RF power signals are locked, and therelative phase between the multiple RF signals is also locked. Examplesof such systems can be found with reference to U.S. Pat. No. 7,602,127,U.S. Pat. No. 8,110,991, and U.S. Pat. No. 8,395,322, assigned to theassignee of the present invention and incorporated by reference in thisapplication.

RF plasma processing systems include components for plasma generationand control. One such component is referred to as a plasma chamber orreactor. A typical plasma chamber or reactor utilized in RF plasmaprocessing systems, such as by way of example, for thin-filmmanufacturing, utilizes a dual frequency system. One frequency (thesource) of the dual frequency system controls the generation of theplasma, and the other frequency (the bias) of the dual frequency systemcontrols ion energy. Examples of dual frequency systems include systemsthat are described in U.S. Pat. No. 7,602,127; U.S. Pat. No. 8,110,991;and U.S. Pat. No. 8,395,322 referenced above. The dual frequency systemsdescribed in the above-referenced patents include a closed-loop controlsystem to adapt RF power supply operation for the purpose of controllingion density and its corresponding IEDF.

Multiple approaches exist for controlling a plasma bias potential andthus the corresponding IEDF. The approaches include: conventionallow-frequency sine wave biasing; multiple sine wave biasing withoutharmonic locking; harmonically locked multiple sine wave biasing; andshaped biasing to create a monotonic or custom IEDF. Each of theseapproaches has associated disadvantages and/or limitations. For example,the low-frequency sine wave biasing approach exhibits a bimodal IEDF(i.e. primarily two non-zero ion energy levels or absolute voltagepotentials over a cycle of a RF bias voltage signal). A monotonic IEDF(i.e. primarily a single non-zero ion energy levels or absolute voltagepotential over a cycle of a RF bias voltage signal) is better than abimodal IEDF for controlling etch profiles and/or etch selectivity.

As another example, the harmonically controlled multiple sine wavebiasing approach may be implemented in high-power implementations, butincludes the use of large expensive generators, which are difficult toisolate from each other when operating at low bias RF frequencies. Theharmonically controlled multiple sine wave biasing approach experiencesinstantaneous high voltage peaks or nulls that affect instantaneous ionenergy levels due to variation in instantaneous plasma sheath voltage.

The shaped biasing approaches can be power limited and also includeslarge expensive power generators. One shaped biasing approach includes abroadband amplifier. It is difficult to properly match a non-linearplasma impedance to a source impedance of the broadband amplifier. Inaddition, a broadband amplifier is typically power inefficient andexpensive.

Another shaped biasing approach includes the use of a switch mode powersupply and current source for generating a bias potential. This approachincludes pulse width modulation and sine wave modulation and is powerand voltage limited due to use of transistors in a half-bridgeconfiguration and corresponding breakdown voltages of the transistors.Only one of the transistors is ON at any moment in time. It is alsodifficult to scale this approach for high power applications, such ashigh aspect ratio (HAR) plasma etch processes.

While the above systems enable a certain degree of control of a plasmaprocess, the continually increasing need for smaller components andincreased yields demand continual improvement over the above-describedapproaches.

SUMMARY

A radio frequency power system is provided that includes bias modules, aswitch, a matching network, and a control module. The bias modules areconfigured to generate respectively direct current (DC) bias voltages.The switch is configured to (i) receive current from the bias modules,and (ii) control flow of the current from the bias modules to generate aradio frequency bias voltage signal. The matching network is configuredto (i) receive the radio frequency bias voltage signal, and (ii) basedon the radio frequency bias voltage signal, supply at least a portion ofa radio frequency output voltage signal to an electrode of a substratesupport in a processing chamber. The control module is connected to theswitch and configured to control a state of the switch based on theradio frequency output voltage signal to shape a waveform of the radiofrequency bias voltage signal.

In other features, a method of operating a radio frequency power systemis provided. The method includes: generating DC bias voltages via biasmodules; receiving current from the bias modules at a switch;controlling flow of the current from the bias modules via the switch togenerate a radio frequency bias voltage signal; receiving the radiofrequency bias voltage signal at a first matching network; based on theradio frequency bias voltage signal, supplying at least a portion of aradio frequency output voltage signal to an electrode of a substratesupport in a processing chamber; and controlling a state of the switchbased on the radio frequency output voltage signal to shape a waveformof the radio frequency bias voltage signal.

In other features, a radio frequency power system for supplying radiofrequency power to an electrode in a substrate support of a processingchamber is provided. The radio frequency power system includes aprocessor and a memory. The memory stores instructions executable by theprocessor and configured to: signal bias modules to generate directcurrent bias voltages; control a state of a switch to generate a radiofrequency bias voltage signal based on the direct current bias voltages;receive a feedback signal including a portion of a radio frequencyoutput signal generated via matching networks based on the radiofrequency bias voltage, where the feedback signal is indicative of aradio frequency voltage at the electrode; and control the state of theswitch based on the feedback signal to provide a predetermined ionenergy distribution function.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description, the claims and the drawings. Thedetailed description and specific examples are intended for purposes ofillustration only and are not intended to limit the scope of thedisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a schematic and functional block diagram of an example of a RFpower system;

FIG. 2 is a plot illustrating examples of a bias voltage signal, acomposite source and bias voltage signal, and a voltage potential at anelectrode of a substrate support;

FIG. 3 is a schematic and functional block diagram of an example of a RFpower system including a transformer in accordance with an embodiment ofthe present disclosure;

FIG. 4 is a plot illustrating an example of a combined envelope voltagesignal and corresponding bias RF voltage signal in accordance with anembodiment of the present disclosure;

FIG. 5 is a schematic and functional block diagram of another example ofa RF power system without a transformer in accordance with an embodimentof the present disclosure;

FIG. 6 is a functional block diagram of an example control module inaccordance with an embodiment of the present disclosure; and

FIG. 7 illustrates a RF voltage generation method in accordance with anembodiment of the present disclosure.

In the drawings, reference numbers may be reused to identify similarand/or identical elements.

DETAILED DESCRIPTION

A RF voltage generation system for setting a voltage potential of anelectrode in, for example, a substrate support (e.g., an electrostaticchuck) of a processing chamber can include a source generator and a biasgenerator. An example of a RF power system 10 including a sourcegenerator 12 and a bias generator 14 are shown in FIG. 1. The sourcegenerator generators a source RF voltage signal at a predeterminedfrequency (e.g., 10-100 mega-hertz (MHz)). The bias generator generatesa bias RF voltage signal at a predetermined frequency (e.g., 100-2000kilo-hertz (kHz)). The source generator and the bias generator haverespective matching networks (e.g., matching circuits 16 and 18). In thecase of the bias generator, the matching network may be a simple lowpass filter in series with a DC blocking capacitor. The outputs of thematching networks are combined to provide a composite voltage signalthat is provided to an electrode in the substrate support. In theexample of FIG. 1, outputs of the matching networks 16, 18 are providedto an electrode 19 in a substrate support 20 (e.g., an electrostaticchuck or other substrate support) in a processing chamber 22. Thesubstrate support supports a substrate (or wafer) 24. The substratesupport may have a capacitance (e.g., electrostatic capacitance C_(ESC)or other capacitance). The source RF signal primarily creates a plasmaand the bias RF signal provide a high-negative sheath voltage toaccelerate ions in plasma in the processing chamber. The ions aredirected at a substrate disposed on the substrate support to perform anetching process and/or create, for example, high aspect ratio featuresin the substrate.

The examples set forth herein include RF voltage generation systems thatprovide high-power and shaped plasma sheath voltage waveforms, whichcontrol IEDFs. The RF voltage generation systems generate a flatperiodic and highly negative plasma sheath voltage while providing amonotonic IEDF. In order to provide a flat periodic and highly negativebias RF voltage at a plasma sheath, output voltages of the source andbias generators are pre-distorted to account for plasma coupling andparasitic components of the RF delivery system. Examples ofpre-distorted bias voltage signal V_(RFBias) 30, composite source andbias voltage signal V_(composite) 32, and a sheath voltage signalV_(RFSheath) 34 are shown in FIG. 2. The voltage amplitude of thehigh-frequency source signal from a source generator tends to be muchsmaller than the low-frequency bias signal from a bias generator, thussignals 32 and 34 are depicted as thick traces as an indication of therelatively low voltage amplitude of the source signal. Peak-to-peakvoltage of the bias voltage signal 30 is, for example, 10,000 V. Thepower associated with the sheath voltage signal 34 is, for example,25-30 kilo-watts (kW). The sheath voltage signal 34 represents a voltagepotential at a point between the capacitance of the substrate supportand the plasma.

FIG. 3 shows a RF power system 100 that includes a bias generator 101, asource generator 104, and matching networks 108, 110. The bias generator101 includes a control module 102, bias modules 106, diodes D_(1-N), atransformer T, and a switch SW. The source generator 104 generates asource RF voltage signal having voltage(s) V_(RFSOURCE) and apredetermined frequency (e.g., 60 MHz or other frequency), which isprovided to the matching network 108. As used herein, the term“voltage(s)” refers to one or more voltages. A particular voltage, suchas V_(RFSOURCE) may change over time, hence the reference of voltage(s)V_(RFSOURCE). The bias modules 106 operate as DC power sources andgenerate respective DC voltage signals at predetermined DC voltages.Thus, the bias modules 106 may be referred to as bias generators. In oneembodiment, one of the bias modules 106 is maintained in an ON statewhile one or more of the other bias modules 106 are transitioned betweenON and OFF states by the control module 102. The ON and OFF times of theone or more other bias modules 106 are determined by the control module102. The outputs of the bias modules 106 are passed respectively throughdiodes D₁-D_(N), where N is an integer greater than or equal to two. Theoutputs of the bias modules 106 are connected to an input of a primarywinding of the transformer T. In one embodiment, the bias modules 106operate as batteries connected in parallel, such that the highest DCvoltage output from the bias modules 106 is provided to the input of theprimary winding. In other words, the output of the one of the biasmodules 106 with the highest DC voltage is provided to the input of theprimary winding. The bias modules 106 may include respective DC powersupplies.

The transformer T includes the primary winding and a secondary winding.An output of the primary winding is connected to a terminal of a switch(e.g., a metal-oxide-semiconductor field-effect transistor (MOSFET)).The switch SW is controlled by the control module 102. The controlmodule 102 may operate the switch SW in a linear mode or a switch mode.During the linear mode, the switch SW is operated as a variableresistance and used to implement a linear regulator. The control module102 and the switch SW operate as a high-speed RF voltage regulator. Thevoltages supplied from the control module 102 to a gate of the switch SWduring the linear mode are within a non-saturated region of the switchSW. During the switch mode, the control module 102 supplies a voltage tothe gate of the switch SW to operate the switch SW in a saturatedregion. During the switch mode, the switch SW is transitioned between ONand OFF states.

While the switch SW is in a partially ON state or full ON state, currentpasses from the bias modules 106, through the diodes_(1-N), through DCblocking capacitor C_(B1), through the primary winding of thetransformer T, and then through the switch SW to a reference (or ground)terminal 111. The DC blocking capacitor C_(B1) prevents saturation ofthe transformer T. The current passing through the primary windinginduces passage of current through the secondary winding of thetransformer T. The secondary winding is connected to the referenceterminal 111 at a first end and to the matching network 110 at a secondend. A RF bias voltage signal having voltage(s) V_(RFBIAS) is generatedbetween the input of the matching network 110 and the reference terminal111. The transformer T is a step-up transformer and thus increases avoltage magnitude of a combined envelope voltage(s) V_(ENVELOPE) to amagnitude of the RF bias voltage(s) V_(RFBIAS).

The matching networks 108, 110 are provided as examples, matchingnetworks of different types and/or configurations may be incorporated inthe RF power system 100 of FIG. 3. The matching network 108 includesvariable capacitors C_(S1), C_(S2) and inductor L_(S). The matchingnetwork 110 includes a low pass filter and a series DC blockingcapacitor C_(B2). The capacitors C_(S2), C_(B2) block DC voltagesassociated with plasma in a processing chamber 112 that can be receivedat outputs of the matching networks 108, 110.

The outputs of the matching networks 108, 110 are connected to eachother and to an electrode 114 of a substrate support 116 and provide aRF output voltage signal having voltage(s) V_(RFOUT). The substratesupport 116 supports a substrate 118 in the processing chamber 112. Theoutputs of the matching networks 108, 110 are also connected to adetector 120. The detector 120 effectively filters out the RF voltagesignal having the voltage(s) V_(RFSOURCE) and provides a detectedvoltage signal having voltage(s) V_(RFBiasSense) associated with thevoltage(s) V_(RFBIAS). The detector 120 and corresponding connectionsprovides a feedback loop for feedback control. The RF output voltagesignal and the detected voltage signal may be referred to as feedbacksignals provided in the feedback loop. In one embodiment, the detector120 includes a low pass filter or a band pass filter and permits passageand detection of frequencies within a predetermined range of one or morefrequencies of the RF bias voltage signal having voltage(s) V_(RFBIAS).In one embodiment, the detector 120 is implemented as a low pass filteror band pass filter. In one embodiment, a frequency of the RF biasvoltage signal having voltage(s) V_(RFBIAS) is 400 kHz and the filterpermits passage of a band of frequencies centered at 400 kHz. In anotherembodiment, the frequency of the RF bias voltage signal is 100 kHz-2MHz.

The control module 102, in addition to receiving the voltage(s)V_(RFBiasSense), may also receive a pulse synchronization signal SYNC.The control module 102 controls the bias modules 106 based on thevoltage(s) V_(RFBiasSense) and the pulse synchronization signal SYNC.For example, timing and duration of ON periods of one or more of thebias modules may be based on the voltage(s) V_(RFBiasSense) and thepulse synchronization signal SYNC. The control module 102 may controlthe frequency and/or duty cycle of the switch SW and thus the frequencyand/or duty cycle of the RF bias voltage signal having voltage(s)V_(RFBias) based on the voltage(s) V_(RFBiasSense) and the pulsesynchronization signal SYNC. Control of the DC bias voltages andparameters of the switch SW allows for precise shaping of the RF biasvoltage signal and thus precise shaping of the RF voltage output signaland result voltage signal received at the electrode 114.

The RF power system 100 may further include memory 130. The memory 130may be used to store set, predetermined and/or detected voltages and/orother operating parameters. The voltages may include V_(ENVELOPE),V_(RFBIAS), V_(RFOUT), V_(RFBiasSense), etc. for each cycle. A cycle mayrefer to a cycle of V_(RFBias) and/or V_(RFOUT). The parameters mayinclude the voltage(s) V_(RFSource) and parameters associated with theswitch SW. The switch parameters may include frequency, duty cycle, ONtimes, OFF times, etc.

Examples of the voltage signals having voltages V_(ENVELOPE), V_(RFBIAS)are shown in FIG. 4. FIG. 4 shows a combined envelope voltage signal 150having voltage(s) V_(ENVELOPE) and corresponding RF bias voltage signal152 having voltage(s) V_(RFBIAS). A shaded (or cross-haired region) 154is shown between the voltage signals 150, 152 and represents the energydissipated through the linear mode operation switch SW of FIG. 3. Theoutputs of the bias modules 106 provide the envelope signal 150, whichprovides an outer envelope that is higher in voltage than thecorresponding RF bias voltage signal 152. The voltage signals 150, 152may be at a low frequency (e.g., 100 kHz-2 MHz).

In one embodiment, the output of each of the bias modules 106 provides astep voltage of the combined envelope voltage signal 150. In the exampleof FIG. 4, the combined envelope voltage signal 150 includes two steps(or voltage levels) 156, 158; one for each bias module. Since two ormore bias modules may be included in the RF power system 100, thecombined envelope voltage signal 150 may include any number of steps.The more bias modules and corresponding steps, the more the combinedenvelope voltage signal 150 matches the corresponding RF bias voltagesignal 152 and the less energy dissipated. By providing multiple DCvoltage steps/levels, the RF power system 100 provides a custom shapedRF bias voltage signal 152. The RF power system 100 may be referred toas a “piecewise” or “segmented” RF power system, since the RF powersystem 100 provides multiple bias voltage steps. This holds true for theother RF power systems described below. Although the RF power system 100is shown as being a capacitively-coupled RF system, the examples setforth herein are applicable to other types of RF power systems, such asinductively-coupled RF systems. Also, although the outputs of thematching networks 108, 110 are shown as being connected to the sameelectrode 114, the output of the matching network 108 may be provided toa different electrode than the output of the matching network 110. Oneof the electrodes that one of the matching networks 108, 110 isconnected to may be located outside of the substrate support. Forexample, one of the electrodes may be connected to a showerhead. Thisalso holds true for the other RF power systems described below.

FIG. 5 shows piecewise RF power system 200 that includes a biasgenerator 201, a source generator 204 and matching networks 208, 210.The bias generator 201 includes a control module 202, bias modules 206,diodes D_(1-N), and a switch SW. The bias generator 201 does not includea transformer. The RF power system 200 may be used when a step-up involtage between the diodes D_(1-N) and the matching network 208 is notneeded. The control module 202, source generator 204, bias modules 206,diodes D_(1-N), the switch SW, and the matching networks 208, 210 mayoperate similar as the control module 102, source generator 104, biasmodules 106, diodes D_(1-N), the switch SW, and the matching networks108, 110 of FIG. 3.

The source generator 204 generates a source RF voltage signal havingvoltage(s) V_(RFSOURCE) and a predetermined frequency. The source RFvoltage signal is provided to the matching network 208. The bias modules206 operate as DC power sources and generate respective bias DC voltagesignals at predetermined DC voltages. Thus, the bias modules 206 may bereferred to as bias generators. Outputs of the bias modules 206 arepassed respectively through the diodes D₁-D_(N). The outputs of the biasmodules 206 are connected to an input terminal of the switch SW. In oneembodiment, the bias modules 206 operate as batteries connected inparallel through the diodes D₁-D_(N), such that the highest DC voltageoutput from the bias modules 206 is provided to the input of the switchSW. In other words, the output of the one of the bias modules 206 withthe highest DC voltage is provided to the input of the switch SW.

The switch may be a MOSFET or other suitable switch. The switch SW iscontrolled by the control module 202. The control module 202 may operatethe switch SW in a linear mode or a switch mode. During the linear mode,the switch SW is operated as a variable resistance and used to implementa linear regulator. The voltages supplied from the control module 202 toa gate of the switch SW during the linear mode are within anon-saturated region of the switch SW. During the switch mode, thecontrol module 202 supplies a voltage to the gate of the switch SW tooperate the switch SW in a saturated region. During the switch mode, theswitch SW is transitioned between ON and OFF states.

While the switch SW is in a partially ON state or a full ON state,current passes from through the switch SW to the matching network 210. ARF output voltage V_(RFBIAS) is generated and provided to the input ofthe matching network 210. Voltage magnitude(s) of the combined envelopevoltage(s) V_(ENVELOPE) may be equal to magnitude(s) of the voltage(s)V_(RFBIAS) minus a voltage drop across the switch SW, which isnegligible when the switch SW is in a full ON state.

The matching networks 208, 210 are provided as examples, matchingnetworks of different types and/or configurations may be incorporated inthe RF power system 200 of FIG. 5. The matching network 208 includesvariable capacitors C_(S1), C_(S2) and inductor L_(S). The matchingnetwork 210 includes a low pass filter and DC blocking capacitor C_(B2).The capacitors C_(S2), C_(B2) block DC voltages associated with plasmain a processing chamber 212 that can be received at outputs of thematching networks 208, 210.

The outputs of the matching networks 208, 210 are connected to eachother and to an electrode 214 of a substrate support 216 and provide aRF output voltage signal having voltage(s) V_(RFOUT). The substratesupport 216 supports a substrate 218 in the processing chamber 212. Theoutputs of the matching networks 208, 210 are also connected to adetector 220. The detector 120 effectively filters out the RF voltagesignal having the voltage(s) V_(RFSOURCE) and provides a detectedvoltage signal having voltage(s) V_(RFBiasSense) associated with thevoltage(s) V_(RFBIAS). The detector 220 and corresponding connectionsprovides a feedback loop for feedback control. In one embodiment, thedetector 220 operates similar as the filter 120 of FIG. 3, includes alow pass filter or a band pass filter, and permits passage offrequencies within a predetermined range of one or more frequencies ofthe RF bias voltage signal having voltage(s) V_(RFBIAS). In oneembodiment, the detector 220 is implemented as a low pass filter or aband pass filter. In one embodiment, a frequency of the RF bias voltagesignal is 400 kHz and the filter permits passage and detection of a bandof frequencies centered at 400 kHz. In another embodiment, the frequencyof the RF bias voltage signal is 100 kHz-2 MHz.

The control module 202, in addition to receiving the voltage(s)V_(RFBiasSense), may also receive a pulse synchronization signal SYNC.The control module 202 controls the bias modules 206 based on thevoltage(s) V_(RFBiasSense) and the pulse synchronization signal SYNC.For example, timing and duration of ON periods of one or more of thebias modules may be based on the voltage(s) V_(RFBiasSense) and thepulse synchronization signal SYNC. The control module 202 may controlthe frequency and/or duty cycle of the switch SW and thus the frequencyand/or duty cycle of the RF bias voltage signal having voltage(s)V_(RFBias) based on the voltage(s) V_(RFBiasSense) and the pulsesynchronization signal SYNC.

FIG. 6 shows a control module 250. The control modules 102, 202 of FIGS.3 and 5 may be implemented as the control module 250. The control module250 may include a pattern module 252, a sheath voltage module 254, abias voltage module 256, a DC voltage module 258, a switch module 260, aprediction module 262, a current state module 264, a comparison module266, and a convergence module 268. In one example embodiment, thecontrol module 250 includes a processor that executes code associatedwith the modules 252, 254, 256, 258, 260, 262, 264, 266, 268. Operationof the modules 250, 252, 254, 256, 258, 260, 262, 264, 266, 268 isdescribed below with respect to the method of FIG. 7.

For further defined structure of the control modules of FIGS. 1, 3 and5-6 see below provided method of FIG. 7 and below provided definitionfor the term “module”. The systems disclosed herein may be operatedusing numerous methods, an example RF voltage generation method isillustrated in FIG. 7. Although the following operations are primarilydescribed with respect to the implementations of FIGS. 3-6, theoperations may be easily modified to apply to other implementations ofthe present disclosure. The operations may be iteratively performed.Although the following operations are shown and primarily described asbeing performed sequentially, one or more of the following operationsmay be performed while one or more of the other operations are beingperformed.

The method may begin at 300. At 302, the control module 250 and/or thepattern module 252 may select a RF voltage pattern for V_(RFBias),V_(RFOUT), and/or a plasma sheath voltage. The control module 250 mayselect the RF voltage pattern to provide a predetermined IEDF (e.g.,monotonic IEDF). Thus, the control module 250 may be referred to as anIEDF controller. This RF voltage pattern may be selected for a recipeand/or etching pattern followed during, for example, etching, cleaning,and/or other substrate processing operation.

At 304, the control module 250 and/or the sheath voltage module 254,based on the selected RF voltage pattern and for a current cycle, maydetermine or select one or more plasma sheath voltages and/or voltagesindicative of the sheath voltages, such as one or more RF outputvoltages for V_(RFOUT). At 306, the control module 250 and/or the biasvoltage module 256 may determine one or more voltages for V_(RFBias)based on the determined or selected one or more plasma sheath voltagesand/or voltages indicative of the sheath voltages.

At 308, the control module 250 may determine, based on the voltage(s)V_(RFBias) and/or other parameters. Some parameters may be determined bythe DC voltage module 258, such as DC bias voltages of bias modules(e.g., the bias modules 106, 206). Other parameters may be determined bythe switch module 260, such as switch parameters. Yet other parametersmay be determined by the prediction module 262, such as predictedvoltage(s) for V_(RFBiasSense). The predicted voltages may be based onprevious voltage(s) for V_(RFBiasSense) and corresponding determinedand/or selected voltages and parameters. This information may be storedin a memory (e.g., one of the memories 130, 230). In one embodiment,this information is stored in tabular form relating the predictedvoltage(s) to the other parameters.

At 310, the control module 250 and/or the DC voltage module 258 controlsthe bias modules to generate the DC bias voltages to define the outer RFbias voltage envelope to be followed. In one embodiment, one of the biasmodules is left in an ON state. For this embodiment, the control module250 and/or the DC voltage module 258 may activate one or more of theother bias modules, depending on the corresponding step being providedin the current cycle. The number of bias modules activated during acycle may depend on the complexity of the RF voltage waveform beinggenerated. The bias modules being activated during the current cycle maybe activated in a sequential manner. When one or more bias modules arebeing activated, one or more other bias modules may be deactivated.Operation 310 may be performed while operation 312 is performed.

At 312, the control module 250 and/or the switch module 260 controls astate of the switch SW to provide the RF bias voltage signal having thevoltage(s) V_(RFBias). This may include controlling a voltage providedto the gate of the switch, an ON time of the switch, an OFF time of theswitch, and/or duration(s) in one or more states. The RF bias voltagesignal is provided to an electrode of a substrate support via a matchingnetwork.

At 314, a filter (e.g., one of the filters 120, 220) receives an RFvoltage output signal having voltage(s) V_(RFOUT) and/or other detectedvoltage signal having voltages indicative of the plasma sheath voltage.In one embodiment, the voltage at the electrode is detected and providedto the filter. At 316, the filter filters the received voltage signal toprovide a detected voltage signal having voltage(s) V_(RFBiasSense). Thevoltage(s) V_(RFBiasSense) are received at the control module.

At 318, the control module 250 and/or the current state module 264 maystore in the memory the voltage(s) V_(RFBiasSense) and corresponding RFoutput voltage(s) V_(RFOUT), the DC bias voltages, and the switchparameters. At 320, the control module 250 and/or the comparison module266 compares the detected voltage(s) V_(RFBiasSense) to the predictedvoltage(s) V_(RFBiasSense) to determine difference values for thecurrent cycle. At 322, the control module 250 and/or the comparisonmodule 266 may store the difference values in the memory.

At 324, the control module 250 and/or the convergence module 268 adjustsone or more of the DC bias voltages and/or parameters of the switch fora next cycle based on (i) the difference values for the current cycle,(ii) difference values for a previous one or more cycles, and (iii)adjustments made based on results of the previous one or more cycles.Adjusting the DC bias voltages may include adjusting other parameters,such as ON times, OFF times, and/or durations in ON and OFF states ofthe bias modules. At 326, the control module 250 and/or the convergencemodule 268 may store the adjusted DC bias voltages and/or otherparameters adjusted during operation 324. The adjustments made based onvoltages, parameters and/or adjustments of previous cycles provides afeedforward method of converging on a waveform of the selected RFvoltage pattern. The error from previous cycles is used to increase therate of convergence. The control module 250 and/or the convergencemodule 268 in receiving the output of the filter and making the statedadjustments performs as a high-speed regulator.

At 328, the control module 250 may determine if another RF voltage cycleis to be generated for the currently selected RF voltage pattern. Ifanother RF voltage cycle is to be generated, operation 310 is performed,otherwise operation 330 may be performed. At 330, the control module 250may determine if another RF voltage pattern is to be selected. Ifanother RF voltage pattern is to be selected, operation 302 may beperformed, otherwise the method may end at 332.

The above-described operations are meant to be illustrative examples;the operations may be performed sequentially, synchronously,simultaneously, continuously, during overlapping time periods or in adifferent order depending upon the application. Also, any of theoperations may not be performed or skipped depending on theimplementation and/or sequence of events.

The RF power systems disclosed herein include fewer hardware componentsthan traditional RF power systems such as the RF power systemspreviously described for the sine wave biasing, multiple sine wavebiasing, and broadband amplifier/shaped biasing approaches. Thisdecreases associated operating costs and increases reliability. Thedisclosed RF power systems also provide increased operating efficiencyover the multiple sine wave and broadband amplifier/shaped biasingapproaches. There is less wasted energy to heat due to use of multipleDC bias modules, which can be 90% efficient. The disclosed RF powersystems are applicable to high voltage (e.g., greater than or equal to−10,000 V) applications and provide monotonic IEDFs for high aspectratio (HAR) etching. HAR etching is used to manufacture 3D NAND flashmemory devices, high density dynamic random access memory (DRAM)devices, and other memory devices, such as phase change random accessmemory (PCRAM). In one embodiment, the RF power systems may beimplemented to precisely control low ion energy processes, such asatomic layer etch and atomic layer deposition processes. These processesare utilized in semiconductor logic processing and multi-patterninglithography processing.

The foregoing description is merely illustrative in nature and is in noway intended to limit the disclosure, its application, or uses. Thebroad teachings of the disclosure can be implemented in a variety offorms. Therefore, while this disclosure includes particular examples,the true scope of the disclosure should not be so limited since othermodifications will become apparent upon a study of the drawings, thespecification, and the following claims. It should be understood thatone or more steps within a method may be executed in different order (orconcurrently) without altering the principles of the present disclosure.Further, although each of the embodiments is described above as havingcertain features, any one or more of those features described withrespect to any embodiment of the disclosure can be implemented in and/orcombined with features of any of the other embodiments, even if thatcombination is not explicitly described. In other words, the describedembodiments are not mutually exclusive, and permutations of one or moreembodiments with one another remain within the scope of this disclosure.

Although the terms first, second, third, etc. may be used herein todescribe various elements, components, loops, circuits, and/or modules,these elements, components, loops, circuits, and/or modules should notbe limited by these terms. These terms may be only used to distinguishone element, component, loop, circuit or module from another element,component, loop, circuit or module. Terms such as “first,” “second,” andother numerical terms when used herein do not imply a sequence or orderunless clearly indicated by the context. Thus, a first element,component, loop, circuit or module discussed below could be termed asecond element, component, loop, circuit or module without departingfrom the teachings of the example implementations disclosed herein.

Spatial and functional relationships between elements (for example,between modules, circuit elements, semiconductor layers, etc.) aredescribed using various terms, including “connected,” “engaged,”“coupled,” “adjacent,” “next to,” “on top of,” “above,” “below,” and“disposed.” Unless explicitly described as being “direct,” when arelationship between first and second elements is described in the abovedisclosure, that relationship can be a direct relationship where noother intervening elements are present between the first and secondelements, but can also be an indirect relationship where one or moreintervening elements are present (either spatially or functionally)between the first and second elements. As used herein, the phrase atleast one of A, B, and C should be construed to mean a logical (A OR BOR C), using a non-exclusive logical OR, and should not be construed tomean “at least one of A, at least one of B, and at least one of C.”

In the figures, the direction of an arrow, as indicated by thearrowhead, generally demonstrates the flow of information (such as dataor instructions) that is of interest to the illustration. For example,when element A and element B exchange a variety of information butinformation transmitted from element A to element B is relevant to theillustration, the arrow may point from element A to element B. Thisunidirectional arrow does not imply that no other information istransmitted from element B to element A. Further, for information sentfrom element A to element B, element B may send requests for, or receiptacknowledgements of, the information to element A.

In this application, including the definitions below, the term “module”or the term “controller” may be replaced with the term “circuit.” Theterm “module” may refer to, be part of, or include: an ApplicationSpecific Integrated Circuit (ASIC); a digital, analog, or mixedanalog/digital discrete circuit; a digital, analog, or mixedanalog/digital integrated circuit; a combinational logic circuit; afield programmable gate array (FPGA); a processor circuit (shared,dedicated, or group) that executes code; a memory circuit (shared,dedicated, or group) that stores code executed by the processor circuit;other suitable hardware components that provide the describedfunctionality; or a combination of some or all of the above, such as ina system-on-chip.

The module may include one or more interface circuits. In some examples,the interface circuits may include wired or wireless interfaces that areconnected to a local area network (LAN), the Internet, a wide areanetwork (WAN), or combinations thereof. The functionality of any givenmodule of the present disclosure may be distributed among multiplemodules that are connected via interface circuits. For example, multiplemodules may allow load balancing. In a further example, a server (alsoknown as remote, or cloud) module may accomplish some functionality onbehalf of a client module.

The term code, as used above, may include software, firmware, and/ormicrocode, and may refer to programs, routines, functions, classes, datastructures, and/or objects. The term shared processor circuitencompasses a single processor circuit that executes some or all codefrom multiple modules. The term group processor circuit encompasses aprocessor circuit that, in combination with additional processorcircuits, executes some or all code from one or more modules. Referencesto multiple processor circuits encompass multiple processor circuits ondiscrete dies, multiple processor circuits on a single die, multiplecores of a single processor circuit, multiple threads of a singleprocessor circuit, or a combination of the above. The term shared memorycircuit encompasses a single memory circuit that stores some or all codefrom multiple modules. The term group memory circuit encompasses amemory circuit that, in combination with additional memories, storessome or all code from one or more modules.

The term memory circuit is a subset of the term computer-readablemedium. The term computer-readable medium, as used herein, does notencompass transitory electrical or electromagnetic signals propagatingthrough a medium (such as on a carrier wave); the term computer-readablemedium may therefore be considered tangible and non-transitory.Non-limiting examples of a non-transitory, tangible computer-readablemedium are nonvolatile memory circuits (such as a flash memory circuit,an erasable programmable read-only memory circuit, or a mask read-onlymemory circuit), volatile memory circuits (such as a static randomaccess memory circuit or a dynamic random access memory circuit),magnetic storage media (such as an analog or digital magnetic tape or ahard disk drive), and optical storage media (such as a CD, a DVD, or aBlu-ray Disc).

The apparatuses and methods described in this application may bepartially or fully implemented by a special purpose computer created byconfiguring a general purpose computer to execute one or more particularfunctions embodied in computer programs. The functional blocks,flowchart components, and other elements described above serve assoftware specifications, which can be translated into the computerprograms by the routine work of a skilled technician or programmer.

The computer programs include processor-executable instructions that arestored on at least one non-transitory, tangible computer-readablemedium. The computer programs may also include or rely on stored data.The computer programs may encompass a basic input/output system (BIOS)that interacts with hardware of the special purpose computer, devicedrivers that interact with particular devices of the special purposecomputer, one or more operating systems, user applications, backgroundservices, background applications, etc.

The computer programs may include: (i) descriptive text to be parsed,such as HTML (hypertext markup language), XML (extensible markuplanguage), or JSON (JavaScript Object Notation) (ii) assembly code,(iii) object code generated from source code by a compiler, (iv) sourcecode for execution by an interpreter, (v) source code for compilationand execution by a just-in-time compiler, etc. As examples only, sourcecode may be written using syntax from languages including C, C++, C#,Objective-C, Swift, Haskell, Go, SQL, R, Lisp, Java®, Fortran, Perl,Pascal, Curl, OCaml, Javascript®, HTML5 (Hypertext Markup Language 5threvision), Ada, ASP (Active Server Pages), PHP (PHP: HypertextPreprocessor), Scala, Eiffel, Smalltalk, Erlang, Ruby, Flash®, VisualBasic®, Lua, MATLAB, SIMULINK, and Python®.

None of the elements recited in the claims are intended to be ameans-plus-function element within the meaning of 35 U.S.C. § 112(f)unless an element is expressly recited using the phrase “means for,” orin the case of a method claim using the phrases “operation for” or “stepfor.”

What is claimed is:
 1. A radio frequency power system comprising: a plurality of bias modules configured to generate respectively a plurality of direct current (DC) bias voltages; a switch configured to (i) receive current from the plurality of bias modules, and (ii) control flow of the current from the plurality of bias modules to generate a radio frequency bias voltage signal; a first matching network configured to (i) receive the radio frequency bias voltage signal, and (ii) based on the radio frequency bias voltage signal, supply at least a portion of a radio frequency output voltage signal to an electrode of a substrate support in a processing chamber; and a control module connected to the switch and configured to control a state of the switch based on the radio frequency output voltage signal to shape a waveform of the radio frequency bias voltage signal.
 2. The radio frequency power system of claim 1, further comprising a transformer comprising a primary winding and a secondary winding, wherein: the primary winding is configured to receive a combined envelope signal, wherein the combined envelope signal is generated based on the plurality of DC bias voltages; the secondary winding is configured to output the radio frequency bias voltage signal; the switch is connected to the primary winding; and the first matching network is connected to the secondary winding.
 3. The radio frequency power system of claim 2, further comprising a plurality of diodes connected in series respectively with the plurality of bias modules and between the bias modules and the primary winding.
 4. The radio frequency power system of claim 2, wherein the switch comprises: a first terminal connected to the primary winding; a second terminal connected to a reference terminal; and a control terminal connected to the control module.
 5. The radio frequency power system of claim 2, wherein at least one of the plurality of DC bias voltages is combined with another one of the plurality of DC bias voltages to provide the combined envelope signal, which is received at the primary winding.
 6. The radio frequency power system of claim 1, wherein: the plurality of bias modules include a first bias module and a second bias module; and the control module is configured to maintain the first bias module in an ON state and transition the second bias module between ON and OFF states while the first bias module is maintained in the ON state.
 7. The radio frequency power system of claim 1, further comprising: a source generator configured to generate a radio frequency source signal; and a second matching network connected to the source generator, wherein outputs of the first matching network and the second matching network are connected to provide the radio frequency output voltage signal.
 8. The radio frequency power system of claim 1, further comprising a filter configured to filter the radio frequency output voltage signal to generate a detected radio frequency bias signal, wherein: the detected radio frequency bias signal is representative of the at least a portion of the radio frequency output voltage signal; and the control module is configured to control the state of the switch based on the detected radio frequency bias signal.
 9. The radio frequency power system of claim 8, wherein the control module is configured to control states of one or more of the plurality of bias modules based on the detected radio frequency bias signal.
 10. The radio frequency power system of claim 9, wherein the control module is configured to operate the switch in a linear mode, such that the switch is being used as a variable resistance.
 11. The radio frequency power system of claim 9, wherein the control module is configured to operate the switch in a switch mode, such that the switch is operated in a saturated region and is transitioned between ON and OFF states.
 12. The radio frequency power system of claim 1, wherein: the switch is connected to receive the plurality of DC bias voltages in a form of a combined envelope signal; and the first matching network is connected to an output of the switch.
 13. The radio frequency power system of claim 12, wherein at least one of the plurality of DC bias voltages is received at the switch while another one of the plurality of DC bias voltages is received at the switch.
 14. A method of operating a radio frequency power system, the method comprising: generating a plurality of direct current (DC) bias voltages via a plurality of bias modules; receiving current from the plurality of bias modules at a switch; controlling flow of the current from the plurality of bias modules via the switch to generate a radio frequency bias voltage signal; receiving the radio frequency bias voltage signal at a first matching network; based on the radio frequency bias voltage signal, supplying at least a portion of a radio frequency output voltage signal to an electrode of a substrate support in a processing chamber; and controlling a state of the switch based on the radio frequency output voltage signal to shape a waveform of the radio frequency bias voltage signal.
 15. The method of claim 14, further comprising: generating a combined envelope signal based on the plurality of DC bias voltages; receiving the combined envelope signal at a primary winding of a transformer; and outputting the radio frequency bias voltage signal from a secondary winding of the transformer, wherein the switch is connected to the primary winding, and the first matching network is connected to an output of the transformer.
 16. The method of claim 15, further comprising passing current from the plurality of bias modules through a plurality of diodes to the switch, wherein the plurality of diodes are connected in series respectively with the plurality of bias modules and between the bias modules and the primary winding.
 17. The method of claim 14, further comprising: combining at least two of the plurality of DC bias voltages to generate a combined envelope signal; and providing the combined envelope signal to the primary winding.
 18. The method of claim 14, further comprising: maintaining a first bias module in an ON state; and transitioning a second bias module between ON and OFF states while the first bias module is maintained in the ON state, wherein the plurality of bias modules include the first bias module and the second bias module.
 19. The method of claim 14, further comprising: generating a radio frequency source signal; providing the radio frequency source signal to a second matching network; and generating the radio frequency output voltage signal based on outputs of the first matching network and the second matching network.
 20. The method of claim 14, further comprising: filtering the radio frequency output voltage signal to generate a detected radio frequency bias signal, wherein the detected radio frequency bias signal is representative of the at least a portion of the radio frequency output voltage signal; and controlling the state of the switch based on the detected radio frequency bias signal.
 21. The method of claim 20, further comprising controlling states of one or more of the plurality of bias modules based on the detected radio frequency bias signal.
 22. The method of claim 21, further comprising operating the switch in a linear mode, such that the switch is being used as a variable resistance.
 23. The method of claim 21, further comprising operating the switch in a switch mode, such that the switch is operated in a saturated region and is transitioned between ON and OFF states.
 24. The method of claim 14, further comprising: providing the plurality of DC bias voltages to the switch; and providing an output of the switch to the first matching network.
 25. The method of claim 14, further comprising providing at least one of the plurality of DC bias voltages to the switch while providing another one of the plurality of DC bias voltages to the switch.
 26. A radio frequency power system for supplying radio frequency power to an electrode in a substrate support of a processing chamber, the radio frequency power system comprising: a processor; and a memory, wherein the memory stores instructions executable by the processor and configured to signal a plurality of bias modules to generate a plurality of direct current bias voltages, control a state of a switch to generate a radio frequency bias voltage signal based on the plurality of direct current bias voltages, receive a feedback signal including a portion of a radio frequency output signal generated via a plurality of matching networks based on the radio frequency bias voltage, wherein the feedback signal is indicative of a radio frequency voltage at the electrode, and control the state of the switch based on the feedback signal to provide a predetermined ion energy distribution function.
 27. The radio frequency power system of claim 26, wherein the instructions are further configured to: select a radio frequency voltage pattern to provide the ion energy distribution function; and signal the plurality of bias modules and control the state of the switch based on the selected radio frequency voltage pattern.
 28. The radio frequency power system of claim 27, wherein the instructions are further configured to: based on the selected radio frequency voltage pattern, estimate a sheath voltage or a voltage indicative of the sheath voltage; based on the sheath voltage or the voltage indicative of the sheath voltage, determine the radio frequency bias voltage; based on the radio frequency bias voltage, determine the plurality of bias voltages and switch parameters; and control the state of the switch according to the parameters to provide the radio frequency bias voltage signal.
 29. The radio frequency power system of claim 26, wherein the instructions are further configured to: predict a voltage of the feedback signal based on historical values of the feedback signal for one or more previous cycles of the radio frequency bias voltage signal and corresponding parameter values of the radio frequency power system, compare a voltage of the feedback signal for a current cycle of the radio frequency bias voltage signal to the predicted voltage to provide a difference value, wherein the feedback signal is a filtered version of the radio frequency output signal, and based on the difference value, adjust one or more of the plurality of direct current bias voltages or operation of the switch for a next cycle of the radio frequency bias voltage signal.
 30. The radio frequency power system of claim 29, wherein the instructions are further configured to: access one or more difference values for the previous one or more cycles of the radio frequency bias voltage signal, wherein each of the one or more difference values is a difference between respective predicted voltage of the feedback signal and a respective detected voltage; and based on the one or more difference values, adjust the one or more of the plurality of direct current bias voltages or operation of the switch for the next cycle of the radio frequency bias voltage signal.
 31. The radio frequency power system of claim 29, wherein the instructions are further configured to: access one or more adjustment values for the previous one or more cycles, wherein each of the one or more adjustment values corresponds to one of the plurality of direct current bias voltages or operation of the switch; and based on the one or more adjustment values, adjust the one or more of the plurality of direct current bias voltages or operation of the switch for the next cycle of the radio frequency bias voltage signal.
 32. The radio frequency power system of claim 26, wherein the instructions are further configured to adjust ON times of one or more of the plurality of bias modules based on the feedback signal.
 33. The radio frequency power system of claim 26, wherein the instructions are further configured to adjust a frequency and a duty cycle of the switch based on the feedback signal.
 34. The radio frequency power system of claim 26, wherein the instructions are further configured to: select a radio frequency voltage pattern to provide the predetermined ion energy distribution function; and select which of the plurality of bias modules to activate for a cycle of the radio frequency bias voltage signal based on the feedback signal and the selected radio frequency voltage pattern. 